Method and apparatus for manufacture of nylon rods, shapes and tubes



y 1960 J. E. HOLT 2,934,788

METHOD AND APPARATUS FOR MANUFACTURE OF NYLON RODS, SHAPES AND TUBES Filed July 30, 1958 4 CAPSTAN INVENTOR aha United States Patent O METHOD AND APPARATUS FOR MANUFACTURE OF NYLON RODS, SHAPES AND TUBES John E. Holt, Hampton, Conn., assignor to The Danielson Manufacturing Company, Danielson, Conn., a corporation of Rhode Island Application July 30, 1958, Serial No. 752,057

1 Claim. (Cl. 18-475) This invention relates to the method and apparatus for manufacture of nylon rods, shapes and tubes, and particularly to such a method in which an extruded rod, shape or tube of nylon is drawn from an over-size dimension down to the size desired.

In the forming of nylon rods and tubes having diameters greater than about it is generally possible to obtain satisfactory results from extrusion under carefully controlled conditions, without need for an additional sizing step. Sizes in the range from about down, however, are found to be made best by other methods, particularly that in which the rod or tube is extruded freely at a size somewhat larger than the desired final size and is then drawn through a die which causes it eventually to assume the desired size. James et al. Patent No. 2,661,499, Dec. 8, 1953, disclosed one such method and discussed certain problems arising in the practice thereof.

The principal object of the present invention is to provide a relatively simple, rapid and effective process of forming nrylon shapes and tubes, in small sizes, with fewer steps and more accurate and uniform results.

The apparatus used in carrying out the method is shown in the diagrammatic drawings herein, which do not purport to disclose any critical details or dimensions.

Fig. 1 represents conventionally a motor-driven extruder, the extrusion from which is taken up on a reel;

Fig. 2 is a flow diagram representing the elements of the apparatus by which the method is carried out;

Fig. 3 represents an elevation of any one of the partitions or baffles A, B, C, E and F, which are identical;

Fig. 4 represents an elevation of the partition or bafile D in which is mounted a sizing die.

In operation, the nylon material is melted and extruded freely from the extruder as a rod, shape or tube (hereinafter called rod), such free extrusion having, for instance, a diameter 5% to 12% larger than that of the desired final product. It is generally convenient to reel up the over-size extrusion (Fig. l) for storage until needed, but the extrusion may, if desired, be fed directly to the sizing apparatus in which case the Reel of Fig. 1 (i.e., the Pay-in Reel" of Fig. 2) is eliminated. The extruded over-size rod, either from the pay-in reel (Fig. 2) or from the extruder (Fig. 1), is passed through an oil bath which is maintained at a temperature of 300 to 350 F. (roughly 100- -25 below the melting point of the nylon) in order thoroughly to preheat the material, the oil bath being bounded at its ends by partitions or baflles B, C (Figs. 2 and 3) and the rod being preferably passed under guides to control its path through the oil. From the oil bath the heated rod passes immediately through a sizing die spaced a short distance from the end C of the bath which die is located in the partition D and maintained at approximately room temperature by means of a water bath extending from partition D to partition E. The space between C and D prevents the latter from being heated. The opening in the die should have a diameter slightly smaller (e.g., by 3%) than that of the desired final product. The sponge adjacent the' partition E wipes the water oif the rod so that it is practically dry when it passes the partition F.

The rod is drawn through the sizing die by means of a suitable capstan which draws the rod at a rapid speed (e.g., 70 feet per minute) and feeds it to a takeup reel. The rod formed as above described shows no orientation and has no substantial tendency toward further growth (a growth of less than 1% having been observed after several months exposure to atmosphere).

As a specific example, in order to make A rod from nylon having a melting point of about 425 F., the material is extruded through an extruder die to produce a rod having a diameter of .12 to .14 the tolerance at this stage being relatively liberal. The rod is passed (immediately or not) through an oil bath maintained at a constant temperature of about 325 F. and is then drawn through a water-cooled (room temperature) .121" diameter sizing die by the operation of the capstan. The rod thus formed has a finished diameter of .125" with a tolerance of $001", and is subject to growth with time only to the extent mentioned above.

The rather high temperature preheating treatment evidently so conditions the nylon that it can take its full and final set when drawn through the chilled sizing die and subjected to chilling during the time it takes to travel from the die through the water bath. The reason for the air gap between the hot oil and the chilled die is to provide insulation between heating and cooling. Since the heated material passes through the die at a very rapid rate, there is no substantial cooling in the die even though the die is maintained close to normal room temperature. However, the simultaneous drawing down and reduction in temperature as it emerges into cold water increases the tensile strength so that the force required to continue orientation of the material as it emerges from the die is greater than the force required to partially orient the heated material as it is drawn through the die, thus completely eliminating any tendency to neck down and become oriented. There is no danger of such an occurrence in operation according to the examples given above.

It will be understood that nylons melting at temperatures higher or lower than 425 F. may be used and that the temperature of the oil bath may be raised or lowered, more or less in proportion to such variation in the melting point. For producing rods, shapes or tubes in sizes larger or smaller than Vs, referred to above, the relative sizes of the freely extruded material, of the sizing die and of the final product bear substantially the same relation to each other as previously explained.

As mentioned above, it has been found quite practicable to store the oversize rod stock for one or more days before heating in the oil bath and drawing down to the desired size, with no perceptible effect on the result.

In selecting a suitable oil, a major consideration is the flash point which must be safely above the temperature to be reached in the bath. An oil having a flash point of about 550 F. is satisfactory.

As noted above, the term rod is defined and used herein as including also shapes and tubes. The method described and claimed is adaptable particularly to the manufacture of simple shapes, and can be used to bring small tubes to desired sizes within close tolerances.

What I claim is:

The method of making nylon rods which consists in providing a freely extruded rod of a size approximately 5% to 12% larger than the desired size, thoroughly heating the rod to a temperature F. :25 below the melting temperature of the nylon used, passing said heated rod immediately through a sizing die less than approximately 5% smaller than the desired size, said References Cited in the file of this patent sizing die being maintained at substantially normal room UNITED STATES PATENTS temperature, and subjecting said sized rod to continued cooling between said sizing die and a drawing means 211941313 Loomls Mar'191940 whereby the god is caused to assume its desired size 5 2661'499 James at 1953 w t ut s bs n i l e g i 

